The decline or likely extinction of large herbivores such as rhinoceroses, hippos, zebras, camels and elephants threaten to create ‘empty landscapes’ in some of the world’s most diverse ecosystems.

“We are facing the prospect that in 20 years some of these large herbivores will have virtually disappeared from many of the world’s grasslands, savannah, deserts and forests, especially in India, Southeast Asia and Africa,” said Dr Thomas Newsome, from the School of Biological Sciences at the University of Sydney.

Dr Newsome is a contributing author to the research findings published in Science Advances on 2 May.

An international team of wildlife ecologists led by Professor William Ripple, from Oregon State University, conducted an analysis of 74 of the world’s largest herbivores, defined as animals over 100 kilograms who consume vegetation to survive.

As a group, herbivores encompass about 4,000 known species and live in many types of ecosystems on every continent except Antarctica.

The researchers looked at key threats, the likelihood of extinction and the ecological consequences of decline.

The twin threat for herbivores is habitat change and hunting by humans. Hunting is for meat consumption, with an estimated 1 billion humans relying on wild meat, and for the global trade in animal parts.

“Australia’s large herbivores including giant kangaroos and hippopotamus-sized marsupials went extinct about 40,000 years ago, soon after people colonised the continent,” said Dr Newsome.

Diprotodon

“Overhunting by people, climate change and altered fire regimes are the most likely causes, and the loss of these large herbivores resulted in dramatic changes to Australia’s vegetation.”

“The widespread loss of herbivores alive today will have a similarly incalculable impact. It would include less food being available for large carnivores such as lions and tigers and more frequent and intense wildfires because herbivores won’t be controlling the vegetation through grazing.

“They also won’t be fulfilling their role of helping to disperse seed as they graze and travel which will lead to much less diversity in the landscape including loss of habitat for many smaller species.”

In 1992 researcher Kent Redford from the University of Florida coined the term ‘empty forest’ to discuss the decline of animals in tropical forests. The new term ‘empty landscape’ recognises that the threat of species loss extends well beyond that habitat.

The report notes that 25 of the largest wild herbivores now occupy an average of only 19 percent of their historical ranges. Competition from livestock production, which has tripled globally since 1980, has reduced access to land, forage and water and raised the risk of the spread of disease.

The researchers call for a coordinated research effort focusing on threatened species in developing countries and the essential involvement of local people in managing protected areas.